Is it allowed to have for example, you, the player, must make everyone happy but everyone is in a bad mood. So you cheer them up with a pacifist gun! (The gun does not harm the people, it makes them happy, obviously not in an illegal way)

I'm not going to say yes or no", but not sure why you need to specifically shoot the people to cheer them up! To me it feels a bit like you've taken the a typical shooter and kept the same mechanics, but just said "the gun shoots good vibes, not bullets". If you love the idea, go ahead with it! But if you fancy a challenge, see if you can come up with something that doesn't involve a gun and shooting.